Hollow endoprosthesis

ABSTRACT

A hollow endoprosthesis including a metal grid network, metal particles mounted at least at junctions of the metal grid network, and a solid metal portion. Each of the metal particles includes a basic body and at least three pins projecting radially from the basic body, and is an integral part of a material forming the grid network.

FIELD OF THE INVENTION

This invention concerns a hollow endoprosthesis for use in a tubularbone.

Endoprostheses for use in a tubular bone have been known for a long timein many designs. They are set in the bones surgically after themedullary space is routed out and are anchored there either withoutcement or with bone cement.

DESCRIPTION OF THE RELATED ART

This invention concerns an endoprosthesis in the first class mentioned,i.e., an endoprosthesis that can be fixed in tubular bones withoutcement. A number of different implants are also known from this class.The only examples referred to here are implants that are produced by themethod described in DE-A-41 06 971. Variations are described in DE-A-19543 530, for example. The implants mentioned are characterized by thefact that they basically have a basic solid metal body, which iscovered, at least partly, by a three-dimensional, open-mesh spatialnetwork structure, into which and through which bone material of thebone tissue surrounding the implant grows after implantation to achievea permanent secondary fixation of the implant in the tubular bone.

These known implants have major advantages compared to implants fixedwith cement. Thus, after complete organization at a number of bonetrabeculae, the implant is embedded almost hanging free in thesurrounding spongiosa, so it can make stress-dependent equalizingmovements in the medullary space, but this is not possible in practicefor an implant that is cemented in, since then discrete layers(bone-cement implant) hit and work against one another. In this case,the layer of bone cement that connects the implant is on the layer ofspongiosa. Equalizing movements under stress cause loosening of the bonecement and hence loosening of the seat of the implant in the bone.

But there can also be problems with the implants fixed without cementdescribed due to the solidity of the basic body, because the implants,on one hand, and the bone, on the other, have very different modulusesof electricity. Thus, the modulus of electricity of the implant is muchhigher than that of the bone, which, despite the favorable freesuspension in the spongiosa, can lead to problems with the loosening ofthe implant.

SUMMARY OF THE INVENTION

On this background, it is the purpose of this invention to propose animplant which has much less of a tendency to be loosened in its seat intubular bones.

This purpose is accomplished, in general, with a hollow endoprosthesis,which consists mainly of a metal grid network, which has metal particlesat least at its junctions, which is made of a basic body and at leastthree pins projecting radially from it which are integral parts of thematerial forming the grid network, and part of which is also composed ofsolid metal.

The design as a hollow implant by the grid network causes a significantadaptation of the modulus of electricity of the endoprosthesis and ofthe bone.

In other words, despite its load-bearing structure, the implant is givena certain elasticity which allows it to react in a quasi-bone-like wayto the stresses that occur.

Metal particles are used to stimulate the growth of the bone materialsurrounding the endoprosthesis, and they give the endoprosthesis anaggressive exterior, whereby the surrounding bone material is stimulatedto bleed and thus to build and organize bone trabeculae into thestructures.

To maintain sufficient stability of the endoprosthesis, it is providedthat part consist of solid metal, but a smaller part than out of thegrid network. This other solid part assumes a guide function for theendoprosthesis, in the area where only small forces must be introducedfrom the endoprosthesis into the bone material. If the hollowendoprosthesis in the invention is designed as a hip shaft of anartificial hip joint, the solid part made of metal forms the distal endof the hip shaft.

It is especially preferred if at least 60% of it is composed of themetal grid network. Accordingly, the remaining 40% is solid, and in thecase of a hip shaft, on the distal part and to a smaller degree in theproximal area for coupling an artificial joint cavity. Thisendoprosthesis therefore has at least a 60% area in which thecorresponding modulus of electricity approximates that of the bone.

To increase mechanical stability while only slightly increasing themodulus of electricity of the section of the endoprosthesis consistingof the grid network, it may an advantage to provide reinforcing bracesmade with the grid network. In the case of a hip shaft prosthesis, forexample, they would run parallel from proximal to distal to the solidmetal distal section.

In summary, it should once more be emphasized that designing a largepart of the endoprosthesis as a metal grid network is essential in termsof equalizing the modulus of electricity, and mounting it with theparticles described is essential in terms of stimulating the growth ofthe bone material surrounding the endoprosthesis for fast, permanentorganization in and through the plane of the surface structure, which ismade of particles and then into the inside of the endoprosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail using two examples ofembodiment.

FIG. 1 shows a hollow endoprosthesis in designed as a hip shaft of anartificial hip joint with particles, shown enlarged, on the outside ofthe grid network, and

FIG. 2 shows a similar view of the hip shaft in FIG. 1 in an alteredembodiment, and

FIG. 3 shows a sectional view along line III—III in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The same reference numbers and letters are used to mark the same partsbelow.

FIG. 1 shows a partial section of a hip joint, hence the femur part ofan artificial hip joint.

The hip shaft 1 has an artificial head 10 of the hip joint, which isconnected by means of a double cone adapter 9 to insertion cones 15 and16 to the solid connecting part 8 of the hip shaft 1 with a receptacle.

The hip shaft 1 mainly consists of a metal grid network 2 with open mesh21 between the pins 18 forming the grid network 2.

At least at the junctions 5, where the pins 18 cross, metal particles 3are provided. They are made integral with the grid network 2, preferablycast in a fine-casting wax-melting method with the grid network.

The sectional enlargement shows particle 3 more clearly. It is composedof a basic body 6 and pins 7 projecting radially from it. This designgives the surface of the hollow endoprosthesis enormous aggressivenesscompared to the bone material surrounding it after implantation in thefemur. This mechanical aggressiveness substantially promotes the growthof the bone trabeculae.

The distal part of the hip shaft 1 here is designed as a solid part 11,which performs a guide function for the endoprosthesis. This guidefunction centers the hip shaft in the medullary space of the femur.

The hollow endoprosthesis shown in FIG. 2 is different from the one inFIG. 1 in terms of two features. Therefore the following will mainlyconcentrate on these different features:

In the form of embodiment shown, reinforcing braces 17 are provided,which run from the proximal end 19 of the hip shaft 1 to the distalsolid part 11. Their arrangement on the grid network 2 is shown in FIG.3, which shows a schematic section along line III—III in FIG. 2. It canbe seen how each reinforcing brace 17 runs in the medial, lateral,dorsal and ventral area of the hip shaft 1. This compensates forstructurally-induced insufficient stability of the grid network 2,whereby the modulus of electricity is also approximated to the modulusof electricity of the bone.

The overall result is fast growth behavior of the hollow endoprosthesisbecause of the enormous mechanical aggressiveness of its outer structurein the area of the grid network 2 and high long-term stability becauseof the design of the overwhelming part as a grid network 2 due to thethen approximated values of the modulus of electricity of theendoprosthesis and the bone.

What is claimed is:
 1. A hollow endoprosthesis comprising: a metal gridnetwork; metal particles mounted at least at junctions of the metal gridnetwork; and a solid metal portion; wherein each of the metal particlesincludes a basic body and at least three pins projecting radially fromthe basic body, the metal particles being an integral part of a materialforming the grid network.
 2. The hollow endoprosthesis in claim 1,wherein the metal grid network forms at least 60% of the hollowendoprosthesis.
 3. The hollow endoprosthesis in claim 2, wherein thehollow endoprosthesis is a hip shaft endoprosthesis and the solid metalportion forms a distal end of the hip shaft.
 4. The hollowendoprosthesis in claim 2, further comprising a plurality of reinforcingbraces made in one-piece with the grid network.
 5. The hollowendoprosthesis in claim 1, wherein the hollow endoprosthesis is a hipshaft endoprosthesis and the solid metal portion forms a distal end ofthe hip shaft.
 6. The hollow endoprosthesis in claim 5, furthercomprising a plurality of reinforcing braces made in one-piece with thdgrid network.
 7. The hollow endoprosthesis in claim 6, wherein thereinforcing braces run from a proximal end to the solid metal portion.8. The hollow endoprosthesis in claim 1, further comprising a pluralityof reinforcing braces made in one-piece with the grid network.
 9. Thehollow endoprosthesis in claim 8, wherein the reinforcing braces runfrom a proximal end to the solid metal portion.
 10. The hollowendoprosthesis in claim 9, wherein the metal solid portion forms adistal end of the endoprosthesis.